TWI545318B - Polymer-derived ceramic gas sensing device and fabricating method thereof - Google Patents

Description

Polymer ceramic gas sensor and manufacturing method thereof

The invention relates to a sensor and a manufacturing method thereof, in particular to a ceramic gas sensor and a manufacturing method thereof.

Generally, gas sensors are distinguished by working principle, and are generally of an electrochemical, solid electrolyte, and semiconductor type. Among them, semiconductor gas sensors have been widely used in gas monitoring of the environment and process because of their high sensitivity, low material cost and good weather resistance.

The semiconductor material is used as a gas sensor, and when the gas is adsorbed on the surface of the semiconductor, since the carrier density of the semiconductor is changed, the conventional semiconductor gas sensor generally uses the resistance change when the semiconductor adsorbs the gas as the sensing. Specific gases and levels in the process or environment. However, in order to obtain better sensitivity and reactivity by using semiconductor materials, most of them require a heating circuit to provide the work required for the semiconductor gas sensor. temperature. However, this high temperature working condition not only causes the energy consumption of the semiconductor gas sensor, but also makes the characteristics of the semiconductor material itself susceptible to temperature, resulting in poor stability and lifetime of the semiconductor gas sensor. Shortcomings of short life.

Accordingly, it is an object of the present invention to provide a polymer ceramic gas sensor for sensing a gas to be tested.

Therefore, the polymer ceramic gas sensor of the present invention comprises: a sensing body, and an impedance measuring unit.

The sensing body is composed of a cesium carbene polymer ceramic material, and a resistance change occurs when the gas to be tested is adsorbed. The sensing body has two elongated sidewalls spaced apart from each other and a connecting two strips The bridging section of the side wall.

The impedance measuring unit is electrically connected to two opposite distal ends of the two elongated sidewalls for measuring a resistance change of the sensing body.

Further, another object of the present invention is to provide a method of fabricating a polymer ceramic gas sensor.

Therefore, the method for fabricating the polymer ceramic gas sensor of the present invention comprises: a pre-crosslinking step, a post-crosslinking step, a sintering step, and an electrical connection step.

The pre-crosslinking step is to mix a polymer polyazoxide precursor with a photoinitiator to form a premix, apply the premix to a surface of a substrate to form a coating, and utilize lithography. The process is such that the coating forms a preformed layer having a predetermined shape.

The post-crosslinking step is to heat treat the preformed layer to thermally crosslink it.

The sintering step is the preforming that will pass the post-crosslinking step The layer is sintered at a temperature of not less than 400 ° C, and the polymer material of the preformed layer is converted into an inorganic ceramic material to obtain a sensing body.

The electrical connection step is to electrically connect the two opposite ends of the sensing body to each other.

The invention has the advantages of using the polymer polyazoxide precursor as the starting material of the inorganic ceramic material, and therefore, can be shaped by lithography before sintering, the process is simple and easy to control, and then can be high by sintering. The molecular material is converted to an inorganic ceramic material, and this material can be used as a gas sensor.

2‧‧‧Sensing ontology

21‧‧‧Long strip side walls

22‧‧‧Bridge section

3‧‧‧ Impedance measurement unit

31‧‧‧First electrical connection unit

32‧‧‧Second electrical connection unit

4‧‧‧Support substrate

51‧‧‧Pre-crosslinking steps

52‧‧‧post-crosslinking steps

53‧‧‧Sintering step

54‧‧‧Electrical connection steps

55‧‧‧Fixed steps

A‧‧‧width

B‧‧‧ Length

w‧‧‧Width

L‧‧‧ length

Other features and effects of the present invention will be apparent from the following detailed description of the preferred embodiments of the accompanying drawings, wherein: FIG. 1 is a schematic diagram illustrating an embodiment of the polymer ceramic gas sensor of the present invention; 2 is a text flow diagram illustrating the manufacturing method of the embodiment of the present invention; FIG. 3 is a resistance-temperature graph illustrating the resistance-temperature relationship of the specific example 1 of the present invention; and FIG. 4 is a resistance-temperature graph illustrating The resistance-temperature relationship of this specific example 2 of the present invention; and Fig. 5 is a graph showing the conductivity-temperature relationship of the specific examples 1 and 2 of the present invention.

The above and other technical contents, features and effects of the present invention will be apparent from the following detailed description of the embodiments.

The polymer ceramic gas sensor of the present invention can be used to sense a gas to be tested. The gas to be tested may be an inert gas, an oxidizing gas or a reducing gas. Specifically, the gas to be tested may be hydrogen (H ₂ ), nitrogen dioxide (NO ₂ ), nitrogen monoxide (NO), ammonia (NH ₃ ), or the like.

Referring to FIG. 1, an embodiment of the polymer ceramic gas sensor includes: a sensing body 2, and an impedance measuring unit 3.

The sensing body 2 is composed of a cerium carbene polymer ceramic material, and since the ceramic material contains nitrogen, it can have preferable semiconductor characteristics. When an electric current is applied to the sensing body 2, electrons may flow through the sensing body 2 to have conductivity; when the sensing body 2 adsorbs a gas to be sensed, the sensing may be caused because the electron channel is reduced. The conductivity of the body 2 decreases (the resistance increases), and the gas to be tested can be sensed by measuring the change in the resistance of the sensing body 2.

In detail, the sensing body 2 has two elongated side walls 21 spaced apart from each other and a bridging section 22 connecting the two elongated side walls 21, so that the shape of the sensing body 2 is H-shaped. Moreover, the width a of the elongated side wall 21 of the sensing body 2 is greater than the width w of the bridging section 22. Preferably, the width a of the elongated side walls 21 is not less than 10 times the width a of the bridging section 22, and the length b of the elongated side walls 21 is not less than 3 times the length L of the bridging section 22.

The impedance measuring unit 3 is electrically connected to the opposite distal ends of the two elongated sidewalls 21 for measuring the resistance change of the sensing body 2 Chemical. Specifically, the impedance measuring unit 3 may be a 4-point probe impedance measuring device, and has a set of one end portions adjacent to the two elongated side walls 21 respectively. The first electrical connection unit 31 is electrically connected, and the other second electrical connection unit 32 electrically connected to the other end adjacent to the two elongated side walls 21, respectively.

When the polymer ceramic gas sensor of the present invention is used for sensing the gas to be tested, the first electrical connection unit 31 can be used to apply a fixed current to the sensing body 2, and the second electrical connection unit 32 is used. Measure the voltage value. Because the control utilizes the sensing body 2 to be H-shaped, and the width a of the elongated sidewalls 21 is greater than the width w of the bridging segments 22, accordingly, the resistance of the bridging segments 22 is greater than the lengths. The electric resistance of the sidewall 21 can be such that the current passing through the bridging section 22 is mainly controlled by the resistance of the bridging section 22, and therefore, when the width a of the elongate sidewall 21 is much larger than the width w of the bridging section 22, The resistivity (ρ) of the sensing body 2 is as shown in the following formula (1).

V: voltage

I: current

L: length of the bridge segment

w: bridge segment width

d: bridging thickness

C: Geometric correction factor (a/w)

a: long strip side wall width

In addition, it is to be noted that the polymer ceramic gas of the present invention Embodiments of the body sensor can also have a support substrate 4. The sensing body 2 can be fixed on the supporting substrate 4, and the sensing body 2 is disposed at a position to be measured by the supporting substrate 4. For example, the supporting substrate 4 can be perforated and suspended. Hanging in the pipe makes it easier to install.

The support substrate 4 is made of a material selected from the group consisting of insulation and having a support, and in order to be applicable to a high temperature test environment, preferably, the support substrate 4 is selected from the group consisting of alumina, ceramics, and the like, which can withstand high temperature. Specifically, the support substrate 4 may be an insulating package for electronic packaging.

Referring to Fig. 2, the manufacturing method of this embodiment of the above polymer ceramic gas sensor will be described below.

First, a pre-crosslinking step 51 is performed to pre-crosslink a liquid organic polycarbazane precursor (SiCN) to form a preformed layer having a predetermined shape.

In detail, the pre-crosslinking step 51 is to mix a liquid organic high molecular polycarbazane (SiCN) precursor with a photoinitiator to obtain a premix. A crucible substrate having a release layer composed of Teflon on the surface was prepared. The premix is coated on the surface of the release layer to form a coating, and the coating is dried.

Then, using a mask having a predetermined pattern (H-type) as an exposure mask of the coating, the coating is subjected to exposure lithography, and the coating is partially cross-linked in the exposed portion, and then the coating is applied. The unexposed portion is removed to obtain a preformed layer having the predetermined pattern.

Next, a post-crosslinking step 52 is performed to thermally re-crosslink the preformed layer to increase the degree of crosslinking of the preformed layer.

The post-crosslinking step 52 is to heat the preformed layer under conditions of not less than 150 ° C, and the preformed layer is thermally crosslinked to increase the degree of crosslinking of the preformed layer. It is worth mentioning that, in order to avoid warpage of the preformed layer during the thermal crosslinking process, the preformed layer may be sandwiched between two quartz sheets, and then the post-crosslinking step is performed to The warp deformation of the preformed layer is avoided.

Then, a sintering step 53 is performed to convert the polymer material of the preformed layer into an inorganic ceramic material.

In detail, the sintering step 53 is: placing the preformed layer subjected to the post-crosslinking step into a high-temperature sintering furnace, and gradually heating to 1400 ° C under an inert atmosphere at a temperature of not less than 400 ° C for sintering. The polymer material of the preformed layer is pyrolyzed into an inorganic ceramic material to obtain a sensing body 2 which is H-shaped as shown in FIG.

The invention utilizes a liquid and crosslinkable polycarbazane polymer precursor mixed with a photoinitiator, so that the shape of the preformed layer can be precisely controlled by a lithography process commonly used in semiconductor processes, and the preform is formed. After the layer is formed, the polycarbazane polymer can be further converted into a ceramic material having semiconductor characteristics by a sintering method, which is not only simple and easy to control, but also can effectively reduce the manufacturing cost of the sensing body 2.

Then, referring to FIG. 1 , an electrical connection step 54 is performed, and an opposite measurement of the opposite ends of the sensing body 2 by an impedance measuring unit 3 is electrically connected to each other to complete the polymer ceramic gas sensor. Production.

In detail, the impedance measuring unit 3 is a four-point probe measuring device having two sets of electrical connecting units electrically connected to the ends adjacent to the two elongated side walls 21, respectively. 31, 32, wherein one set of electrical connection units can apply current to the sense body, and another set of electrical connection units can be used to measure voltage.

In addition, when the polymer ceramic gas sensor of the present invention includes the support substrate 4, a fixing step 55 may be performed before or after the electrical connection step 54, and the sensing is performed by a wire bonding technique. The four corners of the body 2 may be fixed to the support substrate 4.

Next, the polymer ceramic gas sensor of the present invention and its related electrical measurement results will be described in the following two specific examples.

Specific example 1

The manufacturing process of this specific example 1 is substantially the same as that of the embodiment, and the actual operating parameters of the specific one are explained as follows.

A liquid organic polymer polysilazane (SiCN) precursor and 5 wt% 2,2-dimethoxy-2phenylacetophenone (benzoin dimethyl ether, 2,2-Dimethoxy-2) -phenyl acetophenone, DMPA) is mixed to form a premix. Next, the premix is coated on a crucible substrate having a Teflon release layer, dried, and exposed using a mask having a predetermined pattern of H-shape, after which the unexposed portion is removed by acetone. In addition, the preformed layer was obtained. The preformed layer was then thermally crosslinked at 200 ° C for 5 hours. Then, the thermally crosslinked preformed layer is peeled off from the tantalum substrate, and placed in a high temperature sintering furnace, and heated from 400 ° C to 1400 ° C in 15 minutes under nitrogen, followed by 1400 ° C. Sintering is carried out for 10 minutes at a temperature, and the polymer material of the preformed layer is pyrolyzed at a high temperature to be converted into an inorganic ceramic material to obtain a sensing body.

Finally, the sensing body is electrically connected to a four-point probe measuring device to complete the fabrication of the polymer ceramic gas sensor of the specific example 1.

The thickness of the sensing body of the specific example 1 is 138 μm, the length and width of the bridging section are 2 mm and 0.2 mm, respectively, and the length of the elongated side wall is 8 mm.

Specific example 2

The production parameters of the specific example 2 were substantially the same as those of the specific example 1, except that the thickness of the sensing body of the specific example 2 was 38 μm.

Next, the polymer ceramic gas sensors obtained in the specific examples 1 and 2 were each electrically measured.

Referring to Figures 3 to 4, Figures 3 to 4 show that the polymer ceramic gas sensor obtained in the specific examples 1 and 2 is placed in a vacuum chamber, and the environment of the vacuum chamber is made under different temperature conditions. The vacuum is exchanged under the condition of hydrogen, and the impedance value of the polymer ceramic gas sensor when adsorbing and desorbing hydrogen at different temperatures is measured.

As can be seen from FIGS. 3 to 4, the thickness of the sensing body is thick or thin, and the purpose of sensing the gas by measuring the change in resistance can be achieved at room temperature. In addition, when the film thickness of the sensing body is thick (138 μm), its sensing of hydrogen gas exhibits good sensing reproducibility from room temperature to high temperature (1000 ° C). When the film thickness of the sensing body is thin (38 μm), the change in resistance when adsorbing hydrogen is about one order higher than when the film thickness is 138 μm. The film thickness is thinner and the sensitivity to the gas is better. However, when the sensing body film thickness is thin, at a high temperature (>600 ° C), it may fail due to loss of semiconductor characteristics. Therefore, the film thickness of the sensing body can be appropriately adjusted according to the temperature condition of the measurement environment, and a better sensing result is obtained.

Referring to FIG. 5, FIG. 5 is a graph showing the electrical conductivity (σ) calculated by measuring the polymer ceramic gas sensor obtained in the specific examples 1 and 2 under different temperature conditions, and reciprocal of the electrical conductivity (σ). The result of drawing the temperature.

As can be seen from FIG. 5, when the film thickness of the sensing body is large, the temperature is proportional to the conductivity. However, when the film thickness of the sensing body is low, the conductivity measurement result starts to reverse at 785K, and the display is reversed. When the film thickness of the sensing body is low, it will gradually lose its semiconductor characteristics and fail under high temperature conditions.

In summary, the present invention utilizes a liquid and crosslinkable polycarbazane polymer precursor mixed with a photoinitiator, thereby accurately controlling the shape of the preformed layer in a lithographic process commonly used in semiconductor processes. After the preformed layer is formed, the polycarbazide polymer is converted into a ceramic material having semiconductor characteristics by sintering, which is not only simple and easy to control, but also can effectively reduce the manufacturing cost of the sensing body 2, and By using the polycarbazane polymer ceramic material as a sensing material of a gas sensor, gas sensing can be performed over a wide range of ambient temperatures, so that the object of the invention can be achieved.

However, the above is only the preferred embodiment of the present invention, and the scope of the present invention cannot be limited thereto, that is, the simple equivalent change and repair according to the scope of the patent application and the patent specification of the present invention. Decorations are still within the scope of the invention patent.

2‧‧‧Sensing ontology

21‧‧‧Long strip side walls

22‧‧‧Bridge section

3‧‧‧ Impedance measurement unit

31‧‧‧First electrical connection unit

32‧‧‧Second electrical connection unit

4‧‧‧Support substrate

A‧‧‧width

B‧‧‧ Length

w‧‧‧Width

L‧‧‧ length

Claims (10)

A polymer ceramic gas sensor for sensing a gas to be tested, comprising: a sensing body, which is composed of a cesium carbene polymer ceramic material, and generates a resistance change when adsorbing the gas to be tested, the feeling The measuring body has two elongated side walls spaced apart from each other and a bridging section connecting the two elongated side walls; and an impedance measuring unit electrically connected to the opposite distal ends of the two elongated side walls respectively For measuring the resistance change of the sensing body. The polymer ceramic gas sensor of claim 1, wherein the length of the elongated side walls is not less than 10 times the width of the bridging section, and the length of the elongated side wall is not less than the length of the bridging section 3 times the length. The polymer ceramic gas sensor according to claim 1, wherein the sensing body has a thickness of not more than 200 μm. The polymer ceramic gas sensor according to claim 3, wherein the sensing body has a thickness of 20 to 150 μm. The polymer ceramic gas sensor according to claim 1, wherein the impedance measuring unit is a 4-point probe measuring device, and has two sets of electrical connections respectively adjacent to the ends of the two elongated side walls. An electrical connection unit, wherein one set of electrical connection units can apply current to the sense body and another set of electrical connection units can measure voltage. The polymer ceramic gas sensor according to claim 1, further comprising a supporting substrate disposed on one surface of the supporting substrate. A method for manufacturing a polymer ceramic gas sensor, comprising: a pre-crosslinking step of mixing a high molecular polyazide precursor with a photoinitiator to form a premix, applying the premix to a surface of a substrate to form a coating, and utilizing lithography a process of forming the coating into a H-shaped preformed layer; a post-crosslinking step, heat treating the preformed layer to thermally crosslink; and a sintering step to pass the post-crosslinking step The preformed layer is sintered at a temperature of not less than 400 ° C to convert the polymer material of the preformed layer into an inorganic ceramic material to obtain a sensing body; and an electrical connection step of respectively sensing the two bodies of the body Electrically connected to the outside from the end. The manufacturing method of claim 7, wherein the sensing body has two elongated side walls spaced apart from each other and a bridging section connecting the two elongated side walls, the length of the elongated side walls being not less than the bridging The width of the segment is 10 times, and the length of the elongated sidewall is not less than 3 times the length of the bridging segment. The production method according to claim 7, wherein the substrate has a release layer, the premix is formed on the surface of the release layer, and the post-crosslinking step is thermally crosslinked after the preformed layer. The preformed layer is further detached from the release layer. The production method according to claim 7, wherein the premix has a film thickness of not more than 200 μm, the sintering step is from 400 ° C to 1400 ° C, and the pre-formed layer is sintered to be converted into an inorganic ceramic material. .